How to compare two list data in flutter (dart) - flutter

Question

I have a grid data on my page. I want to compare these data to another list like (id 1,2,3,4,5).
GridView.builder(
itemCount: course == null ? 0 : course.length,
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: (MediaQuery.of(context).orientation == Orientation.portrait) ? 3 : 4),
itemBuilder: (BuildContext context, int index) {
return Card(
child:InkWell(
onTap: () {
setState(() {
courseid = course[index]['id'];
coursename=course[index]['name'];
});
addCourse(course[index]['about']);
},
child:Column(
children: <Widget>[
Text((coursedata['courseid'] == course[index]['id']) ? "Added" : ""),
IconButton(
icon: index.isEven ? Icon(Icons.school) : Icon(Icons.book),
iconSize:MediaQuery.of(context).orientation == Orientation.portrait ?30 : 30,
color: index.isOdd ? Colors.amber[800]: Colors.green[800],
onPressed: (){
getcourseData();
},
),
Text(course[index]['name']),
],
),
),
);
},
),
This is another list data gets from a firebase database.
getcourseData() async {
databaseReference.collection(user.email).getDocuments().then((querySnapshot) {
querySnapshot.documents.forEach((result) {
coursedata=result.data;
});
});
}
Both the above lists are compared using data ids.
coursedata['courseid'] == course[index]['id']) ? "Added" : ""
Kindly help on how to compare data in Gride view builder. Currently, only one data show "Added" though there are other data too not showing "Added" in view.

Answer 1

I have created a demo. Change as per your requirement.
import 'package:flutter/material.dart';
void main() =>
runApp(MaterialApp(home: GridViewDemo()));
class GridViewDemo extends StatefulWidget {
#override
_GridViewDemoState createState() => _GridViewDemoState();
}
class _GridViewDemoState extends State<GridViewDemo> {
// already added indices numbers
List<int> alreadyAddedIndices = [3,4,5,6,7];
var courseid = 0;
var coursename = "default";
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text(("GridView Demo")),
),
body: SingleChildScrollView(
child: Column(
children: [
GridView.builder(
itemCount: 5,
shrinkWrap: true,
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: (MediaQuery.of(context).orientation == Orientation.portrait) ? 3 : 4),
itemBuilder: (BuildContext context, int index) {
return Card(
child:InkWell(
onTap: () {
setState(() {
// change as per your code
courseid = index;
coursename=index.toString();
// add index in list if not available
// tapping again, remove index from list
alreadyAddedIndices.contains(index)?alreadyAddedIndices.remove(index):alreadyAddedIndices.add(index);
});
},
child:Column(
children: <Widget>[
Text((alreadyAddedIndices.contains(index)) ? "Added" : ""),
Icon(index.isEven ? Icons.school : Icons.book,
size:MediaQuery.of(context).orientation == Orientation.portrait ?30 : 30,
color: index.isOdd ? Colors.amber[800]: Colors.green[800],),
// course name text
const Text("course Name"),
],
),
),
);
},
),
],
),
),
);
}
}
Output:
Note:
This is a demo code. You can get all the added course ids in alreadyAddedIndices list. Change code as per the need.

Answer 2

The line,
Text((coursedata['courseid'] == course[index]['id']) ? "Added" : ""),
is only comparing one value as you are iterating over only one list. Try calling a method that returns a boolean value or a Text widget by iterating over both the lists. If the function returns false only then do you add to the list. Here is an example of a sudo code that return a Text widget:
_ComparingLists(int id) {
bool temp = false;
for (int i = 0; i < coursedata['courseid'].length; i++) {
if ((coursedata['courseid'][i] == id)) {
temp = true;
break;
} else {
temp = false;
}
}
// student is already enrolled
if (temp == true) {
return Text("Student is enrolled ...");
}
// student is not enrolled
else {
// do your operations like adding to the list here ....
return Text("No match");
}
}
You can call the method by :
_ComparingLists(course[index]['id'])
Hope that helps :)